1. Field of the Invention
The present invention relates to a semiconductor device having a structure with pins of the very large number obtained by jointing a new lead frame to a semiconductor chip, and a method of manufacturing the semiconductor device.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing a semiconductor device, i.e., a semiconductor package in which a semiconductor chip can be connected to a circuit board or the like through an organic substrate having a projecting electrode such as a solder ball.
In FIG. 1, an organic multilayer circuit board a having about two to six layers formed of an organic material is mounted on its surface with a semiconductor chip b. An electrode of the semiconductor chip b and a wiring film c formed on the surface of the organic multilayer circuit board a are connected to each other by wire bonding employing metal wires d or the like.
A solder ball e is provided on a rear surface of the organic multilayer circuit board a and serves as a projecting electrode electrically connected through a through hole i to the wiring film c on the surface of the organic multilayer circuit board a. The solder ball e is faced to the outside through an opening of a solder resist film f. The semiconductor chip b together with the metal wire d are sealed by a sealing resin g.
A semiconductor package j is formed such that the solder balls e formed on the rear surface of the organic multilayer circuit board a is connected to a circuit board h. Being provided with a large number of solder balls e arranged in a grid fashion, the organic multilayer circuit board a is often called a ball grid array (BGA). The semiconductor package j employing the organic multilayer circuit board a is called a BGA package.
The BGA package j employs wire bonding to connect the electrode of the semiconductor chip b with the wiring film c of the organic multilayer circuit board a. Therefore, this arrangement limits reduction of a pitch between electrode pads of the semiconductor chip b.
Moreover, since a processing for forming the projecting electrodes e of the organic multilayer circuit board a employs a method of physically locating the so-called solder balls, the processing encounters the following problems.
1) when the solder balls e are set at predetermined positions, they are easily displaced therefrom. PA1 2) Since the sizes of the solder balls e are selected by using a sieve or a mesh, the sizes thereof tends to be uneven. PA1 3) There is a limit in the ability to achieve of a more minute arrangement pitch between the solder balls e. PA1 4) Since a base of the organic multilayer circuit board a is formed of an insulative substrate, the solder balls e cannot be formed by electroplating which allows the sizes of the solder balls e to be uniform in size and allows pitches therebetween to be more minute. PA1 5) Composition of the soft solder ball is restricted.
The assignee of the present invention proposed a semiconductor package having a structure with pins of a very large number obtained by jointing a new lead frame to a semiconductor chip. A method of manufacturing the above semiconductor package is disclosed in an application filed by the same assignee (U.S. Ser. No. 08/561,245 filed on Nov. 21, 1995).
The semiconductor package is arranged as follows. Specifically, a large number of leads are formed on a surface of a metal base. An insulative film for holding each of the leads is formed at portions other than an inner lead portion. A solder resist film is further formed. A projecting electrode is formed at an end portion of an outer lead portion of each of the leads. Then, the metal base is selectively removed except its outer peripheral joint portion, thereby a lead frame having each of the lead portions separately formed being formed. A semiconductor chip is jointed to an inner lead frame portion of the lead frame. Then, a reinforcement board is bonded to a rear surface of the outer lead portion of the lead frame. The semiconductor chip is sealed with resin. Then, the lead frame is cut at its joint portions to obtain the lead frame. A large number of projecting electrodes are formed in a grid fashion at a peripheral portion around the semiconductor chip
According to this semiconductor package, since the metal base is employed, the leads and the projecting electrodes can be formed by electroplating. As a result, the leads can be formed in a finer pattern and the projecting electrodes can be prevented from being displaced. Moreover, the size of each of the projecting electrodes can be made uniform and the finer pitches therebetween can be achieved, which enables a large-scale integrated circuit (LSI) to be more downsized and to have pins of the very large number.
A process of manufacturing this semiconductor package encounters the following problem.
Since a chemical processing of a ground is difficult when the solder resist film is formed, the solder resist film and the ground are not bonded to each other satisfactorily, which may lead to the peeling off of the solder resist film during fabrication of the semiconductor package.
When the projecting electrodes are formed by plating, the projecting electrodes on the outer periphery side of the semiconductor package become larger than that formed on the inner periphery side thereof, which may prevent the sizes of the projecting electrodes from being uniform.